Question 1

Which of the following best describes the regulatory mechanism of the trp operon in E. coli when tryptophan is abundant in the environment?

Accepted Answer

The repressor binds to the operator with tryptophan as a corepressor, blocking transcription.

Question 2

A mutation in the trpR gene results in a nonfunctional repressor protein. What is the expected outcome for the expression of the trp operon?

Accepted Answer

The operon will be constitutively expressed, regardless of tryptophan levels.

Question 3

Which of the following equations best represents the relationship between enzyme production and tryptophan concentration in a repressible system like the trp operon?

Accepted Answer

$$E = \frac{k}{[Trp]}$$

Question 4

Which of the following is a key feature of attenuation in the trp operon?

Accepted Answer

It relies on the formation of alternative secondary structures in the leader mRNA.

Question 5

A bacterium has a mutation in the operator region of the trp operon (trpOC). What is the most likely effect?

Accepted Answer

The repressor cannot bind, and the operon is always expressed.

Question 6

Which of the following best describes the function of riboswitches in bacterial gene regulation?

Accepted Answer

They are mRNA elements that change conformation upon ligand binding to regulate gene expression.

Question 7

In the context of sRNA-mediated regulation, what is the effect of sRNA pairing with the ribosome binding site (RBS) of an mRNA?

Accepted Answer

It inhibits translation by blocking ribosome access.

Question 8

Which step in the CRISPR/Cas mechanism involves the integration of foreign DNA fragments into the host genome?

Accepted Answer

Spacer acquisition

Question 9

A bacterial cell is exposed to a new phage and survives due to CRISPR/Cas. What is the most likely explanation?

Accepted Answer

The cell integrates a fragment of the phage DNA as a new spacer in its CRISPR locus.

Question 10

Which of the following best explains why adding a wild-type copy of the trpR gene restores regulation in a trpR- mutant, but adding a wild-type operator does not restore regulation in a trpOC mutant?

Accepted Answer

trpR encodes a diffusible repressor protein, while the operator is a DNA sequence that must be present in cis.

Question 11

Which of the following is a direct result of ligand binding to a riboswitch aptamer domain?

Accepted Answer

The mRNA adopts a terminator conformation, halting transcription.

Question 12

Which of the following equations best represents the process of transcription followed by translation?

Accepted Answer

$$DNA \xrightarrow{transcription} RNA \xrightarrow{translation} Protein$$

Question 13

Which of the following is NOT a function of sRNAs in bacteria?

Accepted Answer

Directly catalyzing the synthesis of tryptophan.

Question 14

Which of the following best describes the role of Cas nucleases in the CRISPR/Cas system?

Accepted Answer

They cleave invading viral DNA guided by crRNAs.

Question 15

A bacterium with a mutation that prevents the formation of the 3-4 stem-loop in the trp operon leader sequence would most likely:

Accepted Answer

Fail to terminate transcription in the presence of tryptophan.

Question 16

Which of the following is a real-world application of the CRISPR/Cas system?

Accepted Answer

Targeted genome editing in plants and animals.

Question 17

Which of the following best explains why riboswitches are considered a form of gene regulation at the RNA level?

Accepted Answer

They change mRNA secondary structure to influence transcription or translation.

Question 18

Which of the following is the correct sequence of events in the CRISPR/Cas adaptive immune response?

Accepted Answer

Spacer acquisition → crRNA biogenesis → Target interference

Question 19

Which of the following is a plausible consequence of a mutation that prevents the processing of pre-crRNA into mature crRNAs in the CRISPR/Cas system?

Accepted Answer

The cell cannot target and cleave invading viral DNA.

Regulation of Gene Expression in Bacteria: trp Operon, Attenuation, Riboswitches, sRNAs, and CRISPR/Cas

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